The addition of iodine monofluoride across carbon-carbon double bonds by reaction with ICl and HF in excess HF solvent in the presence of certain Lewis acid catalysts, leads to the preparation of fluoroiodo olefins. When the olefin is highly fluorinated or perfluorinated, the resulting product is a highly fluorinated or perfluorinated fluoroiodide. For example, when the process of the present invention is applied to tetrafluoroethylene (TFE) the product is perfluoroethyl iodide. Perfluoroethyl iodide and other perfluoroalkyl iodides are used as telogens for the telomerization of tetrafluoroethylene to long-chain perfluoroalkyl iodides. Telomerization is a free radical chemical reaction in which one or more molecules of a polymerizable substance (tetrafluoroethylene) combine with another molecule (perfluoroalkyl iodide) called the telogen. Perfluoroalkyl iodides are known compounds useful for making articles of commerce. Pentafluoroethyl iodide (PFEI) is a commercial product widely used as a telogen for preparation of long-chain perfluoroalkyl iodides.
When the reaction is applied to other olefins the fluoro iodo compounds that result are useful as telogens, as is perfluoroethyl iodide, or as intermediates in the syntheses of fluorocontaining organic compounds. For example, perfluoro methyl vinyl ether yields trifluoromethyl 2-iodotetrafluoroethyl ether which is useful as a telogen. Similarily, the process can be used to prepare other compounds of the type RCFICF.sub.2 X, where R is selected from the group consisting of F and C.sub.n F2.sub.n+1, n has a value of 1-10, X is selected from the group consisting of F and OR', and R' is perfluoroalkyl containing up to about 10 carbon atoms, branched or straight, optionally containing in-chain ether oxygen, and having F, SO.sub.2 F, COF, COCl or CO.sub.2 CH.sub.3 as an end group, provided that when X is OR', R is F. The compounds where SO.sub.2 F or CO.sub.2 CH.sub.3 are the end groups are useful as organic intermediates or as telogens.
The known methods of preparation of PFEI and some other perfluoro alkyl iodides, are based on the reaction of IF.sub.5 with a mixture of tetrafluoroethylene and iodine. Another method of preparation of PFEI is a two-step procedure, in which tetrafluorodiiodoethane is first prepared from tetrafluoroethylene and iodine and then converted to pentafluoroethyl iodide by reaction with iodine pentafluoride.
These processes have the disadvantage of requiring IFs, which is prepared from elementary fluorine. Fluorine, as well as iodine pentafluoride, are substances dangerous to handle and expensive.
According to U.S. Pat. No. 3,829,512, PFEI can be prepared by the reaction of TFE or tetrafluorodiiodoethane with the mixture of I.sub.2 /C1.sub.2 and HF at temperatures of 50.degree.-170.degree. C. The reaction is catalyzed by antimony pentafluoride or other pentavalent antimony halides. No mention is made of the use of catalysts other than SbX.sub.5 (X is halogen), or of operation at temperatures below 50.degree. C.